DELANO, Calif. (AP) -- Sheriff's officials have located the wreckage of a helicopter that disappeared in Central California while trying to keep crops from freezing, and they say the female pilot is dead.

Kern County Sheriff's Department spokesman Ray Pruitt said the crash site was found at 9:50 a.m. on Wednesday, about four hours after the helicopter vanished.

Pruitt told the Bakersfield Californian (http://bit.ly/TwNsOn ) that a sheriff's air unit spotted the wreckage in a vineyard with the help of the pilot of another helicopter who had seen the aircraft go down.

The returning pilot had tried unsuccessfully to contact the missing pilot by radio. Sheriff's officials said the search was difficult because of thick fog and limited visibility.

Authorities have not released the victim's name, but said she was in her 40's.

Federal Aviation Administration spokesman Ian Gregor has said the helicopter was returning to Delano Airport in Kern County when it disappeared. It was among three helicopters that were conducting frost control on a local field.

Officials with San Joaquin Helicopter, a Delano-based company, confirmed the helicopter was part of their fleet. During cold spells, helicopters move warmer air down onto threatened crops.

The National Transportation Safety Board and the Federal Aviation Administration are investigating the causes of the crash.